The present invention relates to a nitride semiconductor light emitting device such as a light emitting diode for use in, for example, various types of display devices and lighting equipment, a semiconductor laser diode and the like.
Group III nitride semiconductor (which will be hereafter referred to as “nitride semiconductor”) represented by gallium nitride (GaN) has been used to make practical use of high brightness light emitting diodes (LEDs) which emit light in a wavelength region from ultraviolet to blue or green. Further increase in the brightness of group III nitride semiconductor is predicted and practical use of semiconductor lighting equipment using a white LED which emits light by exciting a fluorescent material by blue light is expected.
Because a substrate formed of GaN is expensive, so-called “hetroepitaxial growth” using a growth substrate formed of sapphire (single crystal Al2O3) or silicon carbide (SiC) is generally used in process steps for fabricating a nitride semiconductor device. In recent years, research and development of nitride semiconductor light emitting diode using a substrate formed of silicon (Si) which can be obtained as a large area substrate at low costs have been promoted (see, for example, T. Egawa et al., Jpn. J. Appl. Phys., Vol. 41 (2002) L663).
Furthermore, as means for forming high quality bulk GaN crystal, a technique for epitaxially growing nitride semiconductor on a so-called SOI (silicon on insulator) substrate in which a Si thin film having a principal surface of a (111) plane orientation is formed over a substrate of Si with an insulating film of silicon oxide (SiO2) interposed therebetween has been proposed (see, for example, Japanese Laid-Open Publication No. 10-287497).
Although the costs can be advantageously cut if silicon (Si) is used for a substrate on which a nitride semiconductor light emitting device is formed, another problem arises. That is, since silicon has a small band gap, i.e., 1.1 eV, the silicon substrate absorbs emitted light having a wavelength in a visible region and thus it is difficult to achieve increase in brightness.